The manufacture of semiconductor devices requires the formation of electrical conductors on semiconductor wafers. For example, electrically conductive leads on the wafer are often formed by electroplating (depositing) an electrically conductive material such as copper on the wafer and into patterned trenches.
Electroplating involves making electrical contact with the wafer surface upon which the electrically conductive material is to be deposited (hereinafter the "wafer plating surface"). To insure a uniform deposition, it is important that the electrical contact with the wafer plating surface be uniform and reliable.
Brogden et al., U.S. Pat. No. 5,227,041 (hereinafter Brogden), teaches a dry contact electroplating apparatus wherein a number of electrical contacts are provided adjacent to a central aperture of a base of the apparatus. Brogden further teaches that the contacts preferably include relatively sharp tips for piercing any insulating substance which may be present on the wafer plating surface. However, even with relatively sharp tips, one or more of the contacts may form a poor electrical connection with the wafer plating surface. This results in nonuniformity of the deposited electrically conductive layer. To determine if one or more poor electrical connections were made with the wafer plating surface, the wafer can be tested to measure the uniformity of the deposited electrically conductive layer. However, wafers exhibiting nonuniformity of the deposited electrically conductive layer must be discarded reducing the yield of the electroplated wafers. Further, it is not practical or cost effective to test every wafer. Thus, it is desirable to have an apparatus for electroplating a wafer which provides uniform electrical contact with the wafer plating surface while at the same time providing a means of readily testing the integrity of the electrical contact with the wafer plating surface before the wafer is electroplated.
Electroplating also requires immersion of the wafer in a plating solution (i.e. a solution containing ions of the element being deposited, for example a solution containing Cu.sup.++). It is important to prevent contamination of the wafer backside (i.e. the surface of the wafer opposite the wafer plating surface) and the wafer edge from the electrolyte (the ions of the element being deposited).
One conventional method of preventing contamination is to use a corrosive solvent immediately following the electroplating to remove contaminants from the wafer backside and the wafer edge. While this method is satisfactory, it requires an extra processing step and the use of hazardous chemicals. A more effective method is to prevent contamination of the wafer backside and the wafer edge in the first place. Accordingly, it is desirable to have an apparatus for electroplating a wafer which avoids contamination of the wafer backside and the wafer edge at any time during the process.
Brogden (cited above) teaches an electroplating apparatus which reduces contamination of the wafer backside and wafer edge during the electroplating process. Referring to FIG. 2 of Brogden, a sealing ring 40 positioned inside electrical contacts 36 forms a sealing connection with the wafer so that contacts 36 and the wafer backside and edge are not exposed to the plating solution. However, particulates and nonuniformities may result in a poor sealing connection with the wafer allowing plating solution to leak past sealing ring 40 to contaminate contacts 36 and the wafer backside and edge. In the event of leakage, the electroplating apparatus must be serviced and the wafer may have to be discarded. Accordingly, the art needs a dry contact electroplating apparatus which eliminates possible leakage of the plating solution and avoids the associated contamination of the contacts and wafer backside and edge.
Another difficulty with immersing the wafer in a plating solution is entrapment of air bubbles on the wafer plating surface. Air bubbles disrupt the flow of electrolytes and electrical current to the wafer plating surface creating nonuniformity in the deposited layer. One conventional method of reducing air bubble entrapment is to immerse the wafer vertically into the plating solution. However, mounting the wafer vertically for immersion into the plating solution adds complexity and hinders automation of the electroplating process. Accordingly, it is desirable to have an apparatus for electroplating a wafer which avoids air bubble entrapment and which is automated.